The invention relates to a variable speed transmission especially a variable speed transmission for motor vehicles.
Various types of variable speed or variable ratio transmissions are known. Transmissions of this kind are used for example in a motor vehicle for changing the rotational speed of an engine with a certain transmission ratio or torque conversion. In addition, a transmission of this kind can ensure the idling of an engine when a vehicle is at rest. Finally, it is possible to reverse the direction of rotation of the drive shaft by means of a transmission.
A simple variable speed transmission can be created by a manual gearbox with an input (drive) shaft, an output shaft, and a countershaft. The drive shaft is connected with the engine by a clutch so that it can be decoupled forcewise from the engine when shifting. A drive gear sits on the drive shaft that drives the countershaft which in turn is nonrotatably connected with other gears. Gears mounted on the countershaft can be meshed with the gears of the drive shaft. Depending on the choice of a speed and hence of one such gear pair, a desired transmission ratio can be created.
The manual gearbox mentioned above has high efficiency, low weight, and is relatively inexpensive because of its simple design. However, no automatic mode can be achieved with a manual gearbox of this kind. In addition, the load between the engine and the input wheels is interrupted with every shift so that the force of the engine cannot be utilized constantly during a continuous acceleration process. In general, the manual gearbox has a relatively low level of comfort. In addition, a separate starting clutch must be provided to decouple the transmission with the input engine.
An automatic transmission is known as a conventional transmission with an automatic mode as the name itself suggests. A conventional automatic transmission usually has a flow converter on the input shaft side that serves as a starting clutch and produces increases in torque in the conversion range. Usually combinations of several planetary transmissions are connected downstream of the converter, said transmissions depending on the positions of individual gears or groups of gears, and perform a torque and rpm conversion as well as a possible reversal of the direction of rotation for a reverse gear. The shifting processes are usually performed by an electrohydraulic control that produces automatic upshifts and downshifts of the individual gears at the correct point in time.
The automatic transmission suffers from relatively high losses and requires a complex design. A transmission of this kind is generally cost-intensive, has a high weight, and requires complex control.
The same disadvantages affect an automatic transmission with an integrated starting clutch. In a transmission of this kind, only the losses can be reduced slightly.
Another alternative for a variable speed transmission is offered by a manual gearbox with automated shifting. In such a transmission, which resembles the manual transmission described above, all of the clutching and shifting processes are performed fully automatically in accordance with the driver""s wishes. In this way, an automatic mode can in fact be achieved but even with this transmission subject to load interruption when shifting cannot be reduced. Otherwise, in the course of an automated shift, a high control effort, especially in engine control, is required. It also requires a starting clutch with similarly automated control.
Another possibility for a variable speed transmission is provided by a stepless automatic transmission with transfer belts or steel thrust belts, or in a transmission of this kind, a planetary transmission with a forward gear and a reverse gear as well as a multiplate clutch and a continuously adjustable primary v-pulley are provided in such a transmission on the drive shaft. The force transfer to a secondary v-pulley on the drive shaft is accomplished for example through a steel thrust belt. By axial displacement of one diagonally opposite disk half of the v-pulley, the effective lever arms become larger or smaller and the transmission ratio can be chosen, depending on the choice of the ratio of the lever arms r1 to r2.
With such a transmission, however, only lower power levels can be transmitted. Such a transmission is not suitable for transmitting high torques.
Finally, a double clutch transmission is known in which two clutches act on a two-part drive shaft with fixed gears. One half shaft is hollow and surrounds approximately half the second half shaft. Loose gears fit on the drive shaft and are connected with the latter by mechanical selector sleeves. In order to shift gears, one clutch must be released and the other engaged at the same time while the mechanical shifting process is completed within the final closing phase of both clutches. The double clutch also acts as a starting clutch.
The disadvantage of such a double clutch transmission is the use of two clutches which must be so designed that they can transmit even the maximum torque that develops.
The goal of the invention is to provide an economical variable-speed gearbox with an automatic mode, which can transmit high torques and avoids complete load interruption when shifting or changing gear.
This goal is achieved by the variable transmission especially for motor vehicles with an input shaft and a output shaft, as well as a first device located between the input shaft and the output shaft, delivering torque and permitting variable rpm transmission ratios, said device in one operating mode ensuring a complete power flow decoupling of the input shaft and the output shaft, and with a second device provided in parallel with the first device for force transmission between the input shaft and output shaft, with which in contrast to the first device, a continuously selectable torque in the range from zero to the maximum applied torque can be transmitted characterized in that the second device comprises a planetary transmission.
Accordingly, in parallel (especially with regard to a power flow) to a first device, therefore essentially to a first transmission, between the input shaft and the output shaft, a second torque-transmitting device is interposed as well with which a continuously selectable torque in the range from zero to the maximum applied torque can be transmitted between these two shafts. The value of the torque can be controlled or regulated.
Since it is possible to have an interruption in the power flow between the input and output shafts in both the first and second devices, it is not necessary to provide a separate clutch any longer between an input motor and the transmission itself. The clutch is already integrated into the gearbox with a corresponding design, and it is not necessary to perform any maintenance. This xe2x80x9cintegrated clutchxe2x80x9d is economical, requires less space for the transmission-engine unit, and reduces the cost of construction as well as maintenance and repair expenses.
An important point regarding the invention consists in the fact that by a suitable control of the second device, such a torque transmission from the input to the output shaft or vice versa can be performed, that no further torque is transmitted through the first unit, and the transmission ratio in this first unit can be easily changed; for example a shiftable spur gear to be brought into or out of engagement with a shaft or another gear can be shifted in a force-free manner. Since a positive connection or torque connection through the second torque-transmitting device can be maintained between the input and output shafts even when shifting the first device, a complete interruption of the load, for example between a drive motor and drive wheels, is effectively prevented. With suitable control of the second device, a load decrease can be kept very small. The driver then gains the impression, even while shifting, that the vehicle is being continuously accelerated or decelerated. A xe2x80x9cjerk effectxe2x80x9d caused by different accelerations can be avoided.
In the variable speed transmission according to the invention, the function of a xe2x80x9chill holderxe2x80x9d can be provided in simple fashion. A hill holder offers the opportunity to remain at rest on a slope or hill without operating the brakes and to initiate a starting process without the risk of rolling backward by a simple accelerator actuation. Finally, the control cost, especially the control cost for digital engine electronics, can be kept low.
In addition, upshifts can be performed without or with only a low lock time and downshifts can be performed during the performance of an upshift or downshift. Therefore, in downshifts it is not necessary to wait until a previously selected shift has been performed. A shift request can be reported through shift curves, authorized shift signals, or a sequential demand unit.
Finally, the present variable speed transmission according to the invention is also suitable for installation in sport vehicles with especially high engine power.
Additional embodiments as well as advantages and features are provided in the subclaims.
An especially simple possibility for performing continuous torque transmission from the input shaft to the output shaft and vice versa is provided by the use of an efficiency unit based on friction, for example a clutch or brake unit. A clutch must be able to operate in a slip mode and be controlled so that depending on the selected clutch pressure and the resultant slip effect, a desired torque can be transmitted and be applied exactly.
One especially preferred embodiment is characterized by the fact that the first device is in the form of a simple variable speed transmission. In this case, it is possible to take advantage of the special advantages of a variable speed transmission, namely its simple design, high efficiency, compact nature, and high force transmission ability.
Especially preferred is an embodiment in which the second device comprises another transmission. A transmission is provided as an especially suitable additional transmission in the torque-transmitting device, preferably a planetary transmission. In a planetary transmission, various transmission ratios can be achieved in simple fashion in a compact manner. In addition, it is possible to reverse the direction of rotation easily for a reverse gear.
Preferably, the clutch engages the ring gear of the planetary transmission.
According to a preferred embodiment, the ring gear must be secured by a locking device or clutch relative to a transmission housing. As a result, a first transmission possibility is provided, for example a first gear. This transmission step then no longer requires implementation by the first device, for example the variable speed transmission.
It is also possible to decouple the planet carriers which in normal operation can be coupled with the output shaft, from the latter, for example by axial displacement thereof. With a simultaneous locking of the planetary transmission, a reverse gear can be engaged. For example, the ring gear is coupled by the clutch with the output shaft. Of course, other design solutions are also possible for a reverse gear function.
According to a preferred embodiment, the sun gear is or can be coupled with the drive shaft and the planet gear carrier. The precisely reversed design solution is also possible depending on the application.
According to another preferred embodiment, the second device, especially the clutch, is affected by a control designed so that the control, especially the pressure regulation for the clutch, can be controlled as a function of the engine rpm and/or the input rpm and/or the gear that has been engaged or called for and/or the input rpm gradient and/or output rpm gradient. If a clutch is used, it can be controlled continuously from the completely decoupled state to the completely engaged state, with clutch slip taking place in such an intermediate state.
The clutch can be designed as a plate clutch. On the one hand it is connected indirectly or directly with the drive or output shaft or the shiftable spur gears mounted on it or the drive housing and on the other hand with a planetary transmission element (sun gear, planet gear carrier, ring gear), with this shaft associated with this planetary transmission element has no direct connection to the drive or output shaft which in turn is connected indirectly or directly with the clutch.
According to an especially preferred embodiment, between the clutch on the one hand and the input or output shaft coupled directly or indirectly thereby or the shiftable spur gears located thereon on the other hand, a shifting device is provided which permits a controllable coupling between the planetary transmission on the one hand and optionally the input or output shaft, the shiftable spur gears mounted thereon, or the transmission housing on the other.
The shifting device for example can be designed as an axially displaceable bushing, coupling hub, or the like which has elements that are releasably nonrotatably connectable with the transmission housing, a part of a shiftable spur gear, or the output or input shaft.
In addition, synchronizing devices can be provided between this shifting device, especially the displaceable sleeve, coupling hub or the like, and the input or output shafts, spur gears, and the like that can be connected with it.
A connection between the shifting device and a shiftable spur gear located on the input or output shafts is possible to implement in an especially simple manner when the spur gear has a hollow shaft that extends through the input or output shaft.
A direct coupling device between the input and output shafts is also advantageous since as a result direct drive can be engaged [with which the respective transmission loss can be avoided.
In particular, the clutch of the torque-transmitting device and/or the switching device can be operated electromechanically and/or hydraulically and/or pneumatically.
Further advantages and features as well as advantageous embodiments will be found in the subclaims.
The invention will now be explained in greater detail with respect to other advantages and features as seen in embodiments and with reference to the enclosed drawings.